1. Field of the Invention
The present invention relates to a process for the preparation of a phosphor, and more particularly, to a process for the preparation of a cerium activated rare earth oxyhalide phosphor.
2. Description of the Prior Art
It has been heretofore known that a cerium activated rare earth oxyhalide phosphor having the following formula: EQU LnOX:xCe
in which Ln is at least one rare earth element selected from the group consisting of Y, La, Gd and Lu; X is at least one halogen selected from the group consisting of Cl, Br and I; and x is a number satisfying the condition of 0&lt;x.ltoreq.0.1, can be employed as a phosphor for a radiographic intensifying screen, since the phosphor gives an emission (spontaneous emission) in the blue light region with the maximum at the wavelength of approx. 440 nm when excited with a radiation such as X-rays. Recently, it has been discovered that said cerium activated rare earth oxyhalide phosphor emits light in the blue region when excited with an electromagnetic wave having a wavelength within the region of 450-900 nm after exposure to a radiation such as X-rays, that is, the phosphor gives stimulated emission. Because of the stimulability thereof, the cerium activated rare earth oxyhalide phosphor has been paid much attention and investigated as a phosphor for a radiation image storage panel employable in a radiation image recording and reproducing method utiilizing a stimulable phosphor, as described in Japanese Patent Provisional Publication No. 55(1980)-12144.
When a radiation image storage panel containing a stimulable phosphor is employed in radiography for the medical diagnosis, it is particularly desired that the sensitivity of the panel to a radiation is made as high as possible to reduce the exposure dose for patient and to facilitate the procedure for converting the stimulated emission to electric signals. Accordingly, it is desired to make the luminance of stimulated emission of the phosphor employed for the panel as high as possible, and to develop an art for enhancing the luminance of stimulated emission of the phosphor as high as possible. As for the above-mentioned cerium activated rare earth oxyhalide phosphor, the same is desired.